The Haze That Could Hurt Your Harvest

Jul 10, 2023

By Jean-Paul MacDonald

The prevalence of smoke from Canadian wildfires in many states bordering Canada during 2023 have raised concerns about its impact on crop growth.This year, the haze arrived earlier in the season compared to previous years, potentially offering some unexpected benefits to plant health. While reduced light intensity due to smoke may hinder photosynthesis in crops, the diffuse light resulting from the haze could help offset or minimize the negative effects.

One of the main concerns is the potential reduction in light availability, which plays a crucial role in crop productivity through photosynthesis. Studies have shown that a 15% decrease in light intensity did not significantly affect corn yield. However, sustained shading of 30-50% has been linked to yield losses. Gases present in the smoke, such as ozone, can also induce plant stress and hinder growth and development, especially with longer exposure.

Particulates, such as ash residues, might deposit on plant tissues, potentially impacting photosynthesis. While high levels of wildfire residues on leaf surfaces could reduce photosynthesis.

The response of major crops like corn and soybean to reduced sunlight may vary due to differences in their photosynthetic processes. Soybean, a C3 plant, is more sensitive to reduced CO2 availability, while corn, a C4 plant, is more affected by limited light.

The grain fill stage in crops is expected to be more vulnerable to reduced sunlight, while the current vegetative stages in many states may be less impacted. It is recommended to monitor soybean fields approaching flowering and observe pod development this season.

For wheat, nearing harvest season, hazy conditions may hinder grain drying and create favorable conditions for disease development, depending on the extent and duration of the haze.

Despite the challenges posed by the wildfire haze, some potential benefits can counterbalance the negatives. Diffuse light can result in lower leaf surface temperatures, which can be advantageous during water stress/drought conditions, reducing water stress injury. Additionally, photosynthesis can optimize

at light intensities of 50-67% of full sunlight, and diffuse light can enhance photosynthesis compared to direct light.

Monitoring trends in light availability and the photothermal quotient (PTQ) throughout the season is crucial. While the accumulated light integral in May and June has exceeded the 10-year average, recent weeks have shown reduced gains. However, the PTQ values in June were higher than normal, potentially indicating increased productivity.

Continued monitoring and updates will provide valuable insights into the ongoing effects of the wildfire haze on crop growth, helping farmers make informed decisions during the summer months.

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